Platform-type wheelchair lifts of various types are employed in vehicles, and typically include a rollstop or other safety barrier at the outboard edge of the platform, to prevent wheelchairs from accidentally rolling off the platform when the platform is out of contact with the ground, such as a "runaway" wheelchair. Such platform safety barriers may be employed with a wide variety of kinds of platform-type wheelchair lifts, such as parallelogram lifts, underfloor lifts, undervehicle lifts, floor-mounted header/telescoping arm lifts, hydraulic sidelifts, rotary wheelchair lifts, dual lift-tube lifts, and the like.
A "runaway" wheelchair is a wheelchair that unexpectedly starts and uncontrollably rolls away. The Urban Mass Transportation Administration (UMTA) Guidelines Specifications for Active Wheelchair Lifts, for example, require an outboard barrier of a lift platform to stop a "runaway" wheelchair from running off the lift platform positioned at an "intermediate transfer level" (i.e., when the lift platform is disposed generally horizontal and elevated at a level to permit a wheelchair to transfer from the lift platform to the vehicle, and vice versa). The barrier must stop a wheelchair that is fully powered, from a standing start. The starting point must be disposed at least 48 inches away from the outboard barrier.
The height of an outboard barrier is very important to its effectiveness as a runaway wheelchair barrier. Testing has shown that in order to stop a fully loaded runaway wheelchair, i.e., an electric wheelchair loaded with a standard UMTA "adult" dummy (total of chair and dummy is 450 lbs.) is started 48" away and accelerated at full power on full battery charge, the barrier must extend at least 7" high or greater above the platform surface. Less than that height, the runaway wheelchair can climb the barrier and crash to the ground typically with the occupant hitting first and the heavy wheelchair following and striking the occupant. Thus a 7" or taller reinforced barrier is preferred, and is most effective when canted inward, typically at about an angle ranging from about 75.degree. to about 89.degree. to the platform floor.
In the under-floor type of wheelchair lift (herein generally "UFL"), the platform is retracted to a storage bay underneath the vehicle floor, and the rollstop is adapted to be retracted along with the rest of the platform assembly. An outboard rollstop is mounted, preferably by a hinge, at the outboard end of the platform. When the platform is above ground level, such as during lift or at the transfer level, the rollstop is positioned generally vertically (the deployed rollstop position) to form an outboard barrier. After the platform reaches ground level, the rollstop is lowered by rotating outwardly to the horizontal position (the ramp position) to allow the wheelchair and occupant to access or depart from the platform.
An example of an UFL employing an outboard platform rollstop is described in our co-pending application Ser. No. 09/065,666 filed Apr. 23, 1998 and entitled UNDERFLOOR WHEELCHAIR LIFT, which application is hereby incorporated by reference. In a lift of this type the platform is supported by bilateral parallelogram linkages from a generally U-shaped carriage frame. The carriage frame is in turn slidably mounted, typically on rollers, to telescope and nest within a U-shaped header frame mounted under the vehicle floor, being extended and retracted by a carriage drive means. With the carriage frame extended from the header frame so that the carriage arms extend outboard of the vehicle body, the platform may be reversibly moved by a lifting means between a transfer level in which it nests between the arms of the carriage frame, to a ground level, in which the platform is guided by the parallelogram linkage to rest on the ground or curb. With the platform at the transfer level nested between the arms of the carriage (and with accessories such as handrails folded or retracted) the carriage frame and platform may be retracted inboard into the header frame, so that it is stowed under the vehicle floor. The available vertical clearance for the carriage/platform mechanism is on the order of 4-41/2".
In the UFL described in the aforesaid application Ser. No. 09/065,666, the rollstop is pivotally mounted to the outboard end of the platform by a piano-type hinge and is raised from its lowered ramp position to its vertical deployed position automatically by action of the platform lift system as the platform begins its ascent to the transfer level. The lift system comprises hydraulically powered lift chains which terminate at fittings on the rollstop, the rollstop thus being held in its vertical deployed position whenever lifting tension is applied to the lift chains.
In a typical UFL installation, such as in a transit-type bus, the rollstop remains in its vertically deployed position as the platform is stowed, and the rollstop overall height is limited to the height of the stair riser, to avoid obstruction of the stairway with the lift in the stowed configuration. This places a limit on the degree of security provided by the rollstop as a typical riser does not exceed 6" and the carriage stowage clearance is typically less than that, on the order of 4-5". In contrast, as described above, a rollstop height of 7" or greater is needed.
Simple removable or manually stowable rollstops place a significant burden upon the vehicle operator, particularly in a public transit setting, since significant operator time is required to deploy and stow the rollstop each time the lift is used.
Accordingly, there is a need in the art for an outboard rollstop which avoids restrictive height limitations for underfloor stowage, and which operates entirely automatically without operator intervention from initial deployment, through the lifting cycle and during return to stowage.